UNIT 2 TOPIC - PHENOLS (1).pdf

Phenols are organic compounds that contain a hydroxyl (-OH) group attached to an aromatic ring. The general formula for a phenol is ArOH, where Ar is an aromatic ring. The simplest example of a phenol is phenol itself, also known as carbolic acid.

Phenols are important compounds in organic chemistry and are used in a variety of industrial and biological applications. They are commonly used as disinfectants, antiseptics, and preservatives due to their antimicrobial properties. They are also used in the production of plastics, pharmaceuticals, and dyes.

Phenols are acidic compounds, meaning that they can donate a proton (H+) to a solvent or a base. This acidity is due to the stability of the phenoxide ion (ArO-), which is formed when a phenol loses a proton. The stability of the phenoxide ion is due to the resonance stabilization of the negative charge over the aromatic ring.

Phenols can undergo a variety of reactions, including electrophilic substitution, oxidation, and esterification. They can also be used as starting materials for the synthesis of more complex organic compounds.

1. UNIT 2
TOPIC
PHENOLS

2. PHENOLS
Theclassoforganiccompoundswhereoneor
morehydroxylgroups(-OH)attachedtoacarbon
atomthatispartofanaromaticringistermedas
Phenols.ThesimplestisPhenol(C
6H
5OH).
PHYSICALPROPERTIES
▪Phenolsaregenerallycolorlesssolidsatroom
temperature.Onexposuretoair,phenolbecomes
reddishincolour.
▪Phenolsareslightlysolubleinwaterandtheir
solubilityincreaseswithanincreasein
temperature.PhenolisalsoknownasCarbolic
acid.

3. PREPARATION OFPHENOLS
DOW’SPROCESS-Heatingchlorobenzenewith
conc.NaOHsolutionat300°Cunderhigh
pressureresultsintheformationofsodiumsalt
ofphenol,whichinacidicmediumliberatesfree
phenol.

4. FROM AROMATIC AMINES
▪Anilineinthepresenceofnitrousacidform
diazoniumsalt;whichinthepresenceofwater
formphenol.

5. FROM CUMEME (AN INDUSTRIAL PROCESS
FOR PREPARATION OF PHENOLS)
▪Benzeneonreactionwithpropeneinthepresence
ofphosphoricacidformisopropylbenzene
(Cumene).
▪TheOxidationofCumeneresultsinthe
formationofCumeneHydroperoxide,whichon
hydrolysisinacidicmediumproducesphenoland
acetone.

7. FROM ALLYL PHENYL ETHER (CLAISEN
REARRANGEMENT)
▪AllylPhenylEtheronheatingundergoesan
intramolecularrearrangementtoformo-allyl
phenolandthereactionisknownasClaisen
rearrangement.
▪

8. CHEMICALPROPERTIES
REACTIONS OF –OH GROUP
▪FORMATION OF SALT
➢Phenolreactswithsodiumhydroxidetoform
salt.

9. REACTION WITH AMMONIA
▪Phenolreactswithammoniaathightemperature
andpressuretoformaniline.

10. FORMATION OF ESTERS
▪Phenolreactswithacidchlorideinaqueousalkalisolutiontogive
phenylesters.
▪Thealkalifirstformsthephenoxideionwhichthenreactswith
theacidchloridetogivephenylester.
▪ReactionofPhenolwithBenzoylchlorideisknownas
SchottenBaumannreaction.

11. FORMATION OF ETHERS
▪PhenolreactswithDimethylsulphateinalkali
solutiontoformanisole(Methoxybenzene).
oREACTIONWITHZINCDUST

12. REACTIONOFBENZENERING
HALOGENATION
▪Phenolreactswithbrominewater(aqueous
bromine)togiveprecipitateof2,4,6-
tribromophenol.

13. NITRATION
▪Phenolreactswithconcentratednitricacidto
formpicricacid.

14. oNITROSATION
▪Phenolreactswithnitrousacid(obtainedfrom
SodiumnitriteandHClat5°C)toformp-
nitrosophenol.
▪p-nitrosophenolonoxidationwithdil.Nitric
acidgivesp-nitrophenol.
▪

15. SULFONATION
▪WhenPhenolistreatedwithconcentrated
sulphuricacidat20°C,o-phenolsulfonicacidis
formed.

16. REIMER-TIEMANNREACTION
Thisinvolvestreatmentofphenolwithchloroform
inaqueoussodiumhydroxidesolutionfollowedby
acid-hydrolysis.Salicylaldehydeisformed.

17. KOLBEREACTION
Phenolreactswithsodiumhydroxidetoformsodium
phenoxide.
Sodiumphenoxidereactswithcarbondioxideat125°Cat6
atmpressurefollowedbyacidhydrolysistoformsalicylic
acid.

18. FRIESREARRANGEMENT
ThePhenolisfirsttreatedwithaceticanhydride
inthepresenceofaqueousNaOHtogivephenyl
acetate.
Theesteristhenheatedwithaluminiumchloride
catalyst;theacylgroupmigratesfromthe
phenolicoxygentoanorthoorparapositionof
thering.

19. REACTION WITH FORMALDEHYDE
WhenPhenolistreatedwithanalkalinesolution
offormaldehyde,amixtureofo-andp-
hydroxybenzylalcoholisformed.

20. OXIDATION
Phenolundergoesoxidationinthepresenceof
chromicacidtoformp-benzoquinone.

21. CATALYTIC HYDROGENTION
Phenoloncatalytichydrogenationgives
Cyclohexanolat160°C.

22. ACIDICNATUREOFPHENOL: AGENERAL
DISCUSSION
Phenolsareacidicinnature.Theacidicnatureof
phenolisattributedtothe+Reffectinphenol.
Dueto+Reffect,theoxygendevelopsapositive
chargeandtherebyregistersreducedholdon
hydrogen.
ThisresultsintheweakeningoftheO-Hbond
andmakestheremovalofhydrogenasproton
(H
+
)tooccurreadilytherebymakingthephenol
acidic.

23. Phenols are much more acidic than alcohols but
less than carboxylic acids.
Phenols are acidic due to the formation of stable
phenoxide ions in aqueous solutions.
For example, phenol itself gives phenoxide ion on
dissociation.

24. The phenoxide ion is stable due to resonance.
Noticethatthenegativechargeisspread
throughoutthebenzeneringandthereby
effectivelydispersed.
This charge delocalization is a stabilizing factor
in the phenoxide ion.

25. Ontheotherhandnoresonanceispossibleinthe
alkoxideion(RO
-
)derivedfromthealcohols.The
negativechargeislocalizedonasingleoxygen
atom.
Consequentlyalcoholaremuchweakeracids
thanphenols.
Alkoxideion

26. EFFECTOFSUBSTITUENTS ONACIDIC
STRENGTH OFPHENOL
Theelectronwithdrawinggroups(forexample
-Cl,-CN,-CHO,-COOH)presentonaromaticringsincrease
theacidicstrengthofphenol.
Theelectronwithdrawinggroupstakewaytheelectrons
fromtheringsystemandthusincreasethepositive
chargeonoxygenofO-Hbond.Morethepositivecharge
onoxygen,easiertheremovalofprotonandhigherthe
acidicstrength.
Theelectronreleasinggroups(-CH
3,-OCH
3,-NH
2)
releaseelectronstowardstheringsystemandthis
neutralizesorreducesthepositivechargeontheoxygen
atomandmakesO-Hbondstrongertherebymakingthe
removalofprotondifficult.
Lesserthepositivechargeonoxygen,higherthestrength
ofO-Hbondandlesseristheacidicstrengthofphenol.

27. STRUCTURE ANDUSESOFPHENOL
Itisusedaspowerfulantisepticinsoapsand
lotions.
Itisusedtosynthesizebakeliteplasticresin.
Itisusedincosmeticsurgeryasanexfoliantto
removelayersofdeadskin.
Itisusedasapreservativeforink.
Itisusedincosmeticindustriesin
manufacturingofsunscreen,skinlightining
creamsandhaircoloringsolutions.

28. STRUCTURE ANDUSESOFCRESOLS
Alkylationofo-cresolgivescarvacolwhichis
strongantibacterialagent.
o-cresolisusedinthesynthesisofmuscle
relaxantdrugMephenesin.
p-cresolisusedintheproductionofbutylated
hydroxytoluene(BHT)whichisanantioxidant.

29. m-cresolisprecursorforvariouscompounds-:
➢SyntheticVitaminE
➢Amylmetacresolusedasantiseptic.
➢Preservativeinsomeinsulins.
p-cresolisusedinthesynthesisofBupranolol
whichisanon-selectivebetablocker.
Chloro-m-cresolisusedashousehold
disinfectant.

30. STRUCTURE ANDUSESOFRESORCINOL
Itisusedasantisepticanddisinfectant.
Itisusedinantidandruffshampoootin
sunscreamcosmetics.
Resorcinolhasbactericidaleffectsandcanbe
usedaspreservativesincosmeticsand
dermatologicaldrugs.
Itisusedformakingwoodglue.

31. It is used as analytical reagent for determination
of ketoses sugar.
It’s ointment (5 to 10 %) is used in the treatment
of psoriasis, eczema.
It is used in the production of plasticizers.

32. STRUCTURE ANDUSESOFNAPHTHOLS
1-NaphtholisaningredientofMolisch’sreagent
whichisusedfordetectingthepresenceof
carbohydrates.
1-Naphtholisaprecursorofvarietyof
insecticideslikecarbanyl.
1-Naphtholisusedtodetectthepresenceof
arginineinproteinsbySakaguchitest.
2-Naphtholisaprecursorforthepreparationof
Sudandye.
2-Naphtholisusedasanantisepticsandin
perfumes.

33. QUALITATIVE TEST FOR PHENOLS
EXPERIMENT PROCEDURE OBSERVATION INFERENCE
1. Ferric Chloride TestTakesmallamount
ofsampleinatest
tubeanddissolveit
in1mlofwater.Add
fewdropsofferric
chloridesolution.
VoiletColor Phenol present
2. PhthaleinTest Placeinadrytest
tube0.5geachofthe
sampleandphthalic
anhydride.
Add2to3dropsof
conc.sulphuricacid.
Heatthetubegently
forabout1minute.
Coolandadd10%
solutiononNaOHin
excess.
Red Color Phenol Present

34. EXPERIMENT PROCEDURE OBSERVATION INFERENCE
3.Bromination Takesmallamount
ofsampleinatest
tubeanddissolveit
in1mlofwater.Add
bromine water
gradually.
First decolourationof
bromine takes place
and on adding in excess
a yellowish –white ppt.
forms.
Phenol present
4. LibermannreactionTake0.5gofthe
sampleinatesttube
andaddfewcrystals
ofsodiumnitrite.
Heatgentlyforhalf
aminute.Cooland
add1mlofconc.
sulphuricacid.
Deep green or violet
coloration develops.
Dilute the mixture with
water, the solution
turns red. Add an
excess of NaOH
solution, the solution
again become green
and blue.
Phenol Present

35. EXPERIMENT PROCEDURE OBSERVATION INFERENCE
5. BenzoylationTakeabout0.2g
ofthesampleina
beaker and
dissolveitin15to
20mlof10%
NaOH solution.
Addabout3mlof
benzoylchloride.
Shakeitvigorously
for10minutes.
Solidseparates
out
Phenolpresent

36. THANK YOU